气门和气门座结合面的研磨采用的是()。
A.平面研磨
B.曲面研磨
C.圆锥面研磨
D.圆柱面研磨
参考答案:C
at failing in the maths exam, John wouldn't like to talk about it to his parents.
A.Disappointing
B.Having disappointed
C.Disappointed
D.To be disappointed
工程车辆能否拉运烟花爆竹等易燃易爆物品?